1. Field of the Invention
The present invention relates to an image forming device such as a laser printer or a copying-machine, and more particularly, to a process cartridge and an image forming device having a photoreceptor drum unit.
2. Description of the Related Art
An image forming device such as a laser printer or a copying-machine has an image forming device body and a process cartridge detachably attached to the body.
The process cartridge is a member which transfers, to recording media such as paper, contents such as characters and graphics to be indicated. This member is equipped with a photoreceptor drum unit on which the content to be transferred is formed. Accordingly, in the process cartridge, various means for forming, on the photoreceptor drum unit, contents to be transferred are also arranged. For example, means respectively performing development, charging, and cleaning can be cited as the various means.
The photoreceptor drum provided in the photoreceptor drum unit is a cylindrical member. While operated, the drum is rotated around the axis of a cylinder. In order to rotate the photoreceptor drum in this way, a gear provided at the side of the image forming device body transmits a driving force through a driving shaft to another gear provided at a member (end member) mounted at an end portion of the photoreceptor drum.
In such a system, particularly, a color machine provided with plural photoreceptor drums has a fear of color shift, color unevenness or the like caused by a deficiency of rotation accuracy. Thus, it is necessary to provide a high-precision gear at the end member.
The cases of applying, in order to deal with this problem, the following two types of driving methods have increased. According to these driving methods, the above problem can be solved without requiring high-precision gears. Not only a color machine but a black-and-white machine has similar advantages.
A first driving method is to put a penetration shaft through the photoreceptor drum and transmit a driving force to the photoreceptor drum using a key-groove or the like. According to this driving method, the high-precision gears for receiving a driving force from the image forming device body are made unnecessary. However, because the penetration shaft is necessary, there are problems that it is difficult to assemble the photoreceptor drum unit, and that the exchange of a photoreceptor drum takes time.
A second driving method is to transmit, without using a penetration shaft, a driving force directly to a coupling provided at an end member mounted at the photoreceptor drum. Several types of this driving method can be cited. Among them, one type of this driving method uses a sliding surface made of a resin as a shaft while a driving force is received at the coupling provided at the end member, or another type thereof supplementarily uses a sliding surface made of a resin as a shaft. According to such a type of using the sliding surface made of a resin as the shaft (including the type of supplementarily using the sliding surface made of a resin as the shaft), accuracy of transmitting a rotating force is high. The assembly of the photoreceptor drum unit and the exchange of the photoreceptor drum are easily achieved.
For example, Japanese Patent No. 4,415,532 discloses a technique of using the sliding surface made of a resin while a driving force is received at the coupling.